Demountable vacuumtight seal



Feb. 3, 1953 R. G. PICARD 2,627,580

DEMOUNTABLE VACUUM-TIGHT SEAL Filed Oct. 25, 1948 l gt, /%/Z r i 46\ f e15 Jill {I [Z 1 1 11 a I z; 1 1 Z! I 17 19 INVENTOR HUBER-r E. PIEARDATTORNEY Patented Feb. 3, 1953 DEMOUNTABLE VACUUMTIGHT SEAL Robert G.Picard, Collingswood, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application October 23, 1948, Serial No. 56,176

4 Claims. 1

This invention relates to demountable vacuumtight seals for high-vacuumapparatus and will be described as applied to an electron-opticalinstrument wherein the seal, when assembled, forms part of a conduitthrough which electrons pass from one lens chamber of the instrument toanother and, when disassembled, permits access 1 to the interior of saidchambers for the purpose of cleaning the same or aligning or replacingthe lens elements therein.

The principal object of the invention is to provide an improvedvacuum-tight seal of the general character described, and onecharacterized by the ease and rapidity with which it may be assembledand disassembled without the use of a wrench or other tool.

Another and important object of the invention is to provide ademountable vacuum-tight connection between the various compartments ofan electron-optical instrument and one which shall provide magnetic andelectrostatic shielding of the space between the said compartments.

The accompanying drawing shows, in vertical section, so much of anelectron-optical instrument as is necessary for a complete understandingof the present invention. Here the demountable jointof the invention,which is indicated generally at I, forms part of a vacuum-tight conduithaving an electron-optical axis .r--:c along which electrons travel froman upper source (not shown) through the magnetic focusing fieldsprovided by a pair of electromagnets 2 and 3 to a lower target (notshown). The magnets 2 and 3 are contained in toroidal shape brasshousings 4 and 5, respectively. The central bore of one or both of thesemagnet housings may contain a pair of pole-pieces 8 and. 9 mounted inpredetermined spaced relation as on a collar I I]. This pole-pieceassembly 8, 9, I is shown maintained within the bore of the upperhousing or conduit member 4 by a small pivoted finger II on the lowerface 4a of the said member and is removable as a unit (e. g. tofacilitate cleaning) when the joint I is dem-ounted. In the instant casethe space between the upper and lower conduit members 4 and is fixed bythe length of a cylindrical pedestal I2 which rests upon the upper majorface So of the lower member 5 and upon which the lower rim portion 4B ofthe upper member 4 rests. The upper conduit member 4 has a sliding fiton the pedestal I2 and this permits a limited degree of lateral movementwhich may be applied to the said conduit member, for purposes ofalignment, by a number (preferably three) of adjusting screws I3 whichextend through the pedestal into contact with a depend-' ent rim 4csurrounding the lower plane face 411 of the said conduit member.

The pedestal I2 upon which the upper conduit member 4 rests is providedwith a door I2a through which access may be had to the demountable jointI of the invention. This joint comprises an expansible-contractibleassembly of two telescopically arranged hollow cylinders I4 and I5 whichis rendered vacuum-tight about its inner circumference by a gasket I6seated in an annular groove II adjacent to the inner end of the cylinderI5 of smaller diameter. The free end of each of the cylinders I4 and I5terminates in an outwardly extending flange I8, I9 respectively, andeach flange is provided on its outer major surface with a circulargroove 20, 2| within which an annular gasket 22, 23 is received. Theoverall length of the telescopic cylinders I4, and I5, when in theirillustrated extended condition, is at least as great as the distancebetween the two axially aligned conduit members 4 and 5 which they serveto connect. The oppositely located flanges I8 and I9 on the cylinders I4and I5, and the gaskets 22 and 23 thereon, are urged into intimatecontact with the end faces 4a and 5a, respectively, of the spaced apartconduit members 4 and 5 by means of a helical spring 24 which is wrappedabout the outer surface of the smaller cylinder l5 so that it exerts itsbiasing force in opposite directions against the inner end of the largercylinder I4 and against the top major surface of the flange I9 of thesmall cylinder I5. Obviously, to remove the joint I from its positionbetween the conduit members 4 and 5 it is merely necessary to push theupper cylinder I4 down against the force of the spring 24 and to removethe telescoped assembly, whereupon all parts of the interior of theconduit are accessible for cleaning.

When, as in the instant case, the joint of the invention forms part of aconduit through which electrons (or other elementary electricallychargedparticles) travel, the telescopic cylinders I4 and I5 and the flanges I8and III thereon, may be constituted of soft iron or equivalent(ferromagnetic) material capable of shielding the interior of theconduit from stray magnetic and electric fields capable of deflecting orotherwise altering the path of the electrons within the circuit.

It will now be apparent that the present invention provides a readilydemountable vacuumtight seal and one especially adapted for use inconnection with electron-optical instruments.

What is claimed is:

1. A demountable joint for connecting two spaced apart electron-conduitmembers mounted in spaced relation along a common axis, said jointcomprising an expansible-contractible assembly of two telescopicallyarranged hollow cylinders adapted. to surround said axis in the spacebetween said conduit members, said hollow cylinders being constituted ofa ferromagnetic material whereby they comprise a magnetic shield forelectrons in their journey between said spaced apart electron-conduitmembers.

2. In an electron microscope including a column portion, a section ofsaid column forming a chamber bounded by end faces, an access openingfor said section, and a door for said opening,

the improvement consisting of a collapsible. unit ends of said cylindershaving annular flanges adapted to be presented to said end faces.

3. Apparatus according to claim 2 wherein a gasket is disposed betweenthe inner and outer cylinders of said unit to provide an air-tight sealbetween the cylinders.

4. Apparatus according to claim 3 wherein said cylinders are composed offerromagnetic material.

ROBERT G. PICARD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,405,287 Cliiford Jan. 31, 19222,246,565 Abercrombie June 24, 1941 2,330,628 Ruska Sept. 28, 19432,445,243 Runge July 13, 1948 FOREIGN PATENTS Number Country Date445,561 France Sept. 6, 1.912

